As opposed to many fuels (e.g., gasoline and diesel) which are liquids at room temperature, cryogenic fuels are low boiling point fuels that require storage at very low temperatures to maintain a liquid state. Examples of cryogenic fuels include natural gas, with a boiling point of about −165° C., and hydrogen, with a boiling point of about −253° C. The general advantages of cryogenic fuels over other fuels may include higher energy density by volume and higher stability of the stored fuel. Natural gas advantages may include reduced greenhouse gas emissions and cost reductions. Due to advantages such as these, many vehicle and power generation applications are moving toward liquid natural gas as a fuel of choice.
Machines that are fueled by cryogenically-stored fuels may include a cryogenic reservoir to store the fuel as a liquid at low temperatures. Such machines may also include fuel delivery components (e.g., pumps, pipes, valves, pressure relief valves, filters, instrumentation, etc.) that may be designed to handle the fuel optimally as a liquid and at cryogenic temperatures below the boiling point of the fuel. However, at the beginning of a fueling cycle, such as when starting the machine from stop, the fuel delivery components may be at ambient temperature, or otherwise at a substantially warmer temperature than the cryogenic temperatures experienced during use. When the cold liquid fuel is initially introduced into the warm fuel delivery components at the beginning of a fueling cycle, heat may be introduced into the fuel due to cooling of the fuel delivery components by contact with the fuel. As a result, some of the liquid fuel may be vaporized leading to two-phase (gas/liquid) flow and undesirable fluid flow effects such as annular flow, slugs, plugs, and bubbles which may negatively impact the operation of the fuel delivery components by shock and vibration. Moreover, the vaporized fuel may be returned to the reservoir, thereby increasing the pressure of the reservoir due to a substantial phase change expansion ratio.
Many attempts have been made to prevent vaporization of liquid fuels in fuel delivery components. One example, as described in U.S. Pat. No. 5,228,295, uses liquid natural gas fuel to precool a pump, an eductor, and a meter prior to delivery of the liquid natural gas to a use device. While effective at achieving the function of precooling the system, the aforementioned system does not reduce or minimize liquid evaporation during precooling of the fuel delivery elements.
There is a need for improved systems for precooling fuel delivery components of machines fueled by cryogenically-stored fuels.